大型层状基岩滑坡软弱夹层演化特征研究——以重庆武隆鸡尾山滑坡为例

EVOLUTION CHARACTERISTICS OF WEAK INTERCALATION IN MASSIVE LAYERED ROCKSLIDES——A CASE STUDY OF JIWEISHAN ROCKSLIDE IN WULONG,CHONGQING

软弱夹层经过长期地质历史演化,性质劣化后形成滑带,对大型层状基岩滑坡的稳定性起重要的控制作用。为了查清软弱夹层形成滑带的演化过程,以重庆武隆鸡尾山滑坡为例,对比研究了山体内软弱夹层的发育规律,将其划分为原生软岩、层间剪切带和滑带3个阶段,并通过岩矿组分含量、物理性质、微结构、物理化学性质和蠕变力学性质试验分析了3个阶段的演化特征。结果表明:从矿物成分演化过程来看,黏土矿物含量增加趋势明显,均值从4. 4%增加到16. 9%;从微结构演化过程来看,微结构由致密变得疏松,孔隙及节理裂隙增多,密度降低了5%～6%,孔隙率升高了108%;从物理化学性质演化过程来看,交换性盐基总含量在原岩中最高,其次是滑带,层间剪切带最低,有机质含量逐渐增大,整个演化环境呈弱碱性。从蠕变剪切强度演化过程来看,软弱夹层的内摩擦角由57. 58°降低到29. 63°,黏聚力由585 k Pa降低到96 k Pa。在此基础上,对鸡尾山滑坡驱动块体最大主剖面的下滑推力进行分析,下滑推力随着长期剪切强度参数的降低而增大,当内摩擦角φ<25°,黏聚力c<129 k Pa时,下滑推力大于0,驱动块体失稳。该研究对受软弱夹层控制的层状基岩滑坡的发育发展过程、失稳机理研究提供了重要的借鉴意义。

The weak intercalation forms a sliding zone after long-term geological evolution and plays an important role in controlling the stability of massive layered rockslides. In order to determine the formation process of the sliding zone,we take the Jiweishan Landslide as an example and analyze the developmental regularities of the weak intercalation. The weak intercalation can be divided into three stages including the original soft rock,the interlayer shear zone and the sliding zone. In addition,we have comparatively studied the evolutionary characteristics of weak intercalation through the laboratory test of the physical properties,physicochemical properties,and physical mechanics properties. As a result,from the view of the mineral composition,the mean value of the clay mineral content is increased from 4.4%to 16.9%. From the view of the physical properties and the microstructure,the density is decreased from 5%to 6%,and the porosity is increased by 108%. It reflects the decreased density and loose structure due to long-term evolution. From the view of the physicochemical properties,the total content of exchangeable salt is the highest in the original soft rock,followed by the sliding zone,whereas the interlayer shear zone exhibited the lowest value. The organic matter content is gradually increased in the alkalescence evolutionary environment. From the view of the shear creep strength,the internal friction angle is decreased from 57.58° to 29.63°,and the cohesion decreased from 585 kPa to 96 kPa. Based on these data,we analyze the change of the residual sliding thrust of the main section of the Jiweishan Landslide driving block. The residual sliding thrust increases with a decrease in the long-term strength parameter. When the internal friction angle φ<25°and cohesion c<129 kPa,the residual sliding thrust of the driving block is greater than zero,and then the driving block is sliding. The conclusions provide an important reference for the study of the development and mechanism of layered rockslides controlled by weak intercalations.